1. Field of the Invention
This invention relates to a method and apparatus for selectively providing electrical current to cathode heater, cathode keeper, and one or more magnets of a thruster system. More particularly, this invention relates to a single power control circuit with output switching capabilities to effectively monitor and control cathode heater, cathode keeper and thruster magnet power levels in ionic thrusters.
2. Description of the Art
A conventional spacecraft thruster, such as a Hall current thruster, utilizes various operating components. These components include a cathode heater, a cathode emitter, a cathode keeper and one or more thruster magnets. Each of these operating components requires power and therefore, has an associated power controller to regulate the amount of power received from the spacecraft power supply. This design is inefficient since the control circuitry requires area and adds additional weight to the system. Therefore it is desirable in satellite and spacecraft applications to minimize the amount of equipment necessary to operate a thruster. Thus, an invention that combines multiple functions using a single apparatus that does not increase the mass of the thruster is advantageous. Various systems for discharge generation and control are summarized below. None of these address the problem of providing a single power converter and distribution circuit for efficient distribution of power to thruster elements.
U.S. Pat. No. 5,075,594 issued Dec. 24, 1991 to Schumacher et al., discloses a hollow cathode capable of self-heating by back ion bombardment to a thermionic emission temperature. Electrons are axially or radially extractable from a plasma by an anode of opposite polarity. A voltage is applied to a keeper electrode disposed between the cathode and the anode to sustain the plasma discharge of the gas between the cathode and keeper electrode. A control electrode is disposed between the keeper electrode and the anode. Application of a negative control electrode voltage, or returning the control electrode to cathode potential, causes the plasma discharge to retract back to the area of the keeper electrode, thereby opening a switch. This patent does not disclose a single distribution and control circuit to control multiple system functions.
U.S. Pat. No. 5,132,597, issued Jul. 21, 1992 to Goebel et al., discloses a hollow cathode plasma switch with a magnetic field. A diverging magnetic field is established between a cathode and a control electrode of a hollow cathode plasma switch to expand the plasma at a passageway through the control electrode, thus significantly increasing the current handling of capability of the switch. This dispersion of the plasma across the control electrode produces a uniform current density such that the total interruptible current can be increased by increasing the grid and anode area. This patent fails to disclose a thruster system that has a single controller for providing power to thruster components.
U.S. Pat. No. 5,357,747, issued Oct. 25, 1994 to Myers et al., discloses a pulsed mode cathode with an internal heater and a low work function material. The cathode is preheated to an operating temperature and then the thruster is fired by discharging a capacitor bank. This patent is hereby incorporated by reference in its entirety herein.
U.S. Pat. No. 5,581,155, issued Dec. 3, 1996 to Morozov et al., discloses a plasma accelerator with closed electron drift. This plasma accelerator has a main annular channel for ionization and acceleration, at least one hollow cathode associated with ionizable gas feed means and an annular anode. This plasma accelerator reduces divergence of the ion beam and increases the density of the ion beam and lifetime of the accelerator. This patent does not disclose an apparatus to distribute converted power.
U.S. Pat. No. 5,605,039, issued Feb. 25, 1997 to Meyer et al., discloses a parallel arcjet starter system for ignition and sustaining an electric arc in an arcjet thruster. This patent is hereby incorporated by reference in its entirety herein.
U.S. Pat. No. 5,646,476, issued Jul. 8, 1997 to Aston, discloses a channel ion source. A gas, ionizable to produce a plasma, is introduced into a channel within an ion source and into a hollow cathode imbedded within the ion source. A heater and keeper electrode power supply is used to establish a hollow cathode and keeper electrode plasma. A discharge power supply is used to cause electrons to flow from the hollow cathode in a predominantly one hundred and eighty degree direction to bombard the channel gas distribution and create a channel discharge plasma. This power supply is not selectively distributed to desired elements.
As can be seen from illustrative background discussed above, there is a need in the thruster industry for an improved method and apparatus for controlling cathode heater, cathode keeper and thruster magnet components of a thruster. The present invention provides a solution to that need in the form of a power control circuit with output switching that is capable of selectively controlling the heater, keeper and magnet functions thereby more efficiently providing and controlling the application of power to the thruster components.